Syringe is one of the most common medical devices. In order to reduce the spread of the blood-borne diseases among the patients, all the countries in the world make law to compulsorily popularize and use disposable syringe. However, current common disposable syringes have defects in that such syringes are often repeatedly used, such syringes are provided without safety means, and the needles thereof are exposed out after injection. Therefore, on one hand the disposable syringes are easily used by the lawbreakers or drug addicts; and on the other hand the syringes supposed to be disposable are often reused, which easily causes the virus spread or raises cross infection. In order to prevent the occurrence that the disposable syringes are re-purchased, re-sold and reused and to avoid the infection of the medical care personnel who may be stuck by the needles when recycling the syringes, all the countries in the world are under the research of self-destruction safety syringe.
Self-destruction safety syringes currently known are mainly plunger piercing type or manual pull-type with syringe needle, and further there is also another type that the needle mount is provided with an automatic spring, in which after the fluid has been injected, the push rod is pushed to the frontmost end of the syringe tube and meantime the needle mount is retracted into the syringe tube together with the syringe needle so as to prevent the syringe needle from protruding out to stick someone. However, all these self-destruction safety syringes still have various defects in their designs.
Chinese Patent CN200980874Y discloses a safety self-destruction syringe, in which the needle mount and the syringe needle can automatically retract into the push tube by providing an automatic retraction means in the push tube. However, this invention neither thoroughly solves the problem of how to compress the compression spring into the lower part of the push tube before use (the inside wall of the push tube is smooth without any object for hooking and thus the compression spring cannot be compressively hooked) nor solves the problem that how the residual fluid can pass through and flow into the needle during injection.
U.S. Pat. No. 5,211,628 discloses a syringe with an automatic retracting means. This syringe adopts a biasing member of spring around the shank portion of the connecting shaft, the spring has an upper end engaged with the top terminal wall of the push rod and a lower end embedded and locked in the brake groove by the biasing member. In addition, an actuating section has a pushing terminal moving together with the puncturing end of the connecting shaft. When the coupling end of the connecting shaft disengages from the outer adjacent area under pressure, the pushing terminal on the spring will move downwardly together with the puncturing end, the pulling terminal can pull the lower end of the spring out of the brake groove. Furthermore, a gasket is placed to bring the bulge ring to the rear chamber of the outer cover to engage with the front wall of the rear chamber so as to provide a resistance for the formation of the gasket. This resistance supports for positioning of the bulge ring so as to prevent the movement of a certain position of the front wall of the back chamber of the gasket in hypodermic or intravenous injection puncture, thereby the bulge ring being allowed to disengage from a certain portion of the back chamber of the syringe, therefore, when the first external force is exerted, the tubular needle gauge can move with the bulge ring in the inside wall of the outer cover. However, this syringe still has some defects: when the smallest part of the snap-latch means and the biggest part of the needle mount form an interference fit with each other, the residual fluid is sealed and cannot circulate, at this moment, if the push rod is pushed forward with a large pressure, the needle punctured subcutaneously will be vibrated and causes pain to the patient injected.
Chinese Patent No. 2817873Y also discloses a self-destruction safety syringe. This syringe uses a spring-back device of a steel needle which is arranged in the outer needle mount to form a needle head assembly connected with the top end of the injection cylinder through threads. This syringe not only has the characteristic of the ordinary disposable syringe with the spring-back steel needle, but also the producing process thereof becomes simple and the assembly is convenient. However, it still cannot solve the problem of the resistance of the end plug, and the spheroidal design of the front end of the end plug also will increase the amount of the residual fluid.
U.S. Pat. No. 6,379,336 provides a self-destruction safety syringe with an improved structure, however, the structure of the syringe is quite complex and not easy to be assembled. And moreover, the cost is high and the volume of the fluid residual is high, which is unacceptable especially in the case that the injection fluid is expensive.
Although a lot of self-destruction safety syringes have been developed, those syringes have various structural defects, especially lots of residual fluid is sealed when the connection structures form an interference fit with each other. The present invention is aimed to make a further improvement to the structure of the existing self-destruction safety syringes so as to effectively solve the above technical problems.